1. Field of the Invention
The present invention relates to a magnetoresistive head of the type in which sensing current is applied in the thickness direction of the magnetoresistive film, a magnetic disk apparatus provided with said magnetoresistive head, and a process for production of said magnetoresistive head.
2. Description of the Related Art
The magnetic data storage system has been increasing in areal recording density at a surprisingly fast annual rate of 100%. The high recording density requires the magnetic head mounted on the magnetic data storage system to have a higher output, a narrower track width, and a narrower shield-to-shield distance.
The object of increasing output is achieved by improving the performance of the magnetoresistive film. For recording densities up to several gigabits per square inch, an anisotropic magnetoresistive (AMR) film has been used. However, for recording densities higher than that, a giant magnetoresistive (GMR) film is being used now. The magnetoresistive film of next generation for GMR film includes the tunneling magnetoresistive (TMR) film (mentioned in Journal of Magnetism and Magnetic Materials, vol. 139, 1995, pp. L231–L234) and CPP (current perpendicular to the plane)-GMR film (mentioned in Journal of Applied Physics, vol. 89, 2001, pp. 6943–6945) in which current is applied in the direction perpendicular to the plane of the GMR film.
For reduction of track width, attempts are being made to develop a new exposure technology using a lithography apparatus equipped with a light source for shorter wavelength and to develop a new image enhancement technique. Possibility of further reduction in track width (smaller than a quarter micron or even a tenth of micron) is being investigated.
The object of reducing the shield-to-shield distance is hard to achieve for the GMR film of CIP (current into the plane) structure, in which sensing current flows into the plane of the magnetoresistive film. For CIP-GMR head, thin insulating gap films are provided between the shield film and the GMR film, and between the shield film and the electrode film to supply sensing current to the GMR film. Such a thin insulating gap film permits sensing current to leak to the shield film. In order to avoid this shortcoming, an idea of keeping the insulating gap film thick except for the read track part is disclosed in Japanese Patent Laid-open Nos. 111248/1994 and 111008/1996.
By contrast, the object of reducing the shield-to-shield distance is easy to achieve for the GMR film of CPP structure (in which sensing current flows in the direction perpendicular to the plane of the magnetoresistive film). CPP structure needs no insulating gap film unlike that of CIP structure. A magnetic head equipped with a TMR film (which is a magnetoresistive film of CPP structure) is disclosed in Japanese Patent Laid-open No. 213351/1999. According to this disclosure, the object of reducing the shield-to-shield distance is achieved by arranging a TMR element in the pedestal region formed in the upper and lower shields.
The disadvantageous technology (Japanese Patent Laid-open No. 213351/1999) mentions that it is necessary to form the pedestal region in the upper and lower shields in order to reduce the shield-to-shield distance in the case where a TMR film is used. In practice, however, it is also necessary to consider other structure than the read track for practical head structure.
To be concrete, in the production of a magnetoresistive head of CPP structure, it is important to pattern the magnetoresistive film into a desired shape without damage and to suppress leakage of sensing current across the upper and lower shields used as the electrodes.